1. Field of the Invention
This invention relates generally to internal combustion engines and more particularly to a novel and improved method and apparatus for controlling the air-to-fuel ratio of an internal combustion engine.
2. Description of the Prior Art
The advent of large internal combustion engines for use in automobiles, together with increased concern regarding the environment, has produced engine design objectives which are increasingly complicated and often are contradictory - to build powerful, yet relatively inexpensive and reliable engines and associated controls, while at the same time improving economy of operation and lowering the emissions exhausted by the engines.
In the prior art a number of attempts have been made to achieve such objectives, and such attempts have generally been either too expensive or complicated or, if relatively inexpensive, have been undesirably unreliable. Generally, in prior art systems, attempts have been made to analyze the engine exhaust fumes to determine either the oxygen or emission content and, based on the analysis, to feedback signals to relaively complex control circuitry to adjust the air-fuel ratio being supplied to the engine. These approaches have not been optimal because of the expense and complexity of analyzers which must compensate for the effects of such factors as temperature, pressure and humidity changes in order to analyze the components in the exhaust. In addition, the response times of the necessary feedback systems often have been too slow to both maximize economy and minimize emissions to the extent desired. In those cases in which response times have been decreased, the decrease has been achieved by adding sophisticated and relatively expensive feedback circuitry.
One such prior art approach utilizes an oxygen sensor with a very fast response time to detect the oxygen content of the engine exhaust gas. When the sensor detects departures from the stoichiometric composition, the output voltage of the sensor changes. The sensor output voltage is transmitted to an electronic controller which has output signals to a fuel injection device and to a recirculation valve to adjust the air-fuel ratio to the desired value. Although this system reduces emissions, it is relatively expensive and has a slower response time than is desirable.